Magnetic resonance imaging (MRI) is a technique in which an object is placed in a magnetic field and subjected to pulses of the electromagnetic field at a frequency. Conventional MRI systems include a main magnet which generates a strong static magnetic field of a high temporal stability and a high spatial homogeneity within a field-of-view (FOV) where the imaging takes place. Conventional MRI systems also include a gradient coil assembly located in the bore between the main magnet and the RF coil and generating space-varying fields. The gradient coil assembly causes the response frequency and phase of the nuclei of the patient body to depend upon position within the FOV thus providing a spatial encoding of the body-emitted signal. Conventional MRI systems further include RF coil/coils arranged within the bore which emit RF waves and receive resonance signal from the body. The superconducting main magnet is typically used to achieve high field strength; the superconducting main magnet comprises a plurality of concentric coils placed inside a cryostat which is designed to provide a low temperature operating environment for superconducting coils.
MR imaging is used in diagnosis of a wide variety of medical conditions, including osteoarthritis (OA). Existing and emerging osteoarthritis treatments require early detection of the disease. Unfortunately, there are no established non-invasive diagnostic tools for the early detection of OA or for monitoring the effectiveness of OA therapies. Such a tool is needed to increase the efficacy and effectiveness of treatment. One indicator of OA is proteoglycan depletion. Some studies have shown that cartilage proteoglycan content is indicated by T1ρ relaxation values. These studies theorize that an increase in T1ρ indicates proteoglycan depletion. In MR, T1ρ is the exponential decay constant that describes a decay of transverse magnetization during RF spin lock that causes a spin-lattice relaxation in the rotating frame. The spin-lattice relaxation in the rotating frame probes the slow motion interactions between motionally restricted water molecules and the local macromolecular environment. T1ρ quantification has also been applied to the MR imaging of muscle, breast, liver, brain, spine, and tumors and has shown diagnostic promise in these areas as well.
Conventional quantitative T1ρ imaging is predominantly a single slice method in which only one transverse image of an object is generated. Multislice two-dimensional (2D) and three-dimensional (3D) methods have been suggested that generate multiple transverse images of the internal structure of the object. However both the suggested 2D and 3D methods require retrospective correction of either T2ρ saturation or T1-weighting. Retrospective correction, which necessarily assumes a constant T2ρ or T1 value, can adversely affect quantitative accuracy. Quantitative accuracy is especially adversely affected in imaging of non-homogeneous anatomy such as the brain. Quantitative T2ρ and T1 maps could be acquired but this greatly increases complexity of the experiment.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a more effective method of diagnosing osteoarthritis. There is also a need for a multi-slice quantitative T1ρ imaging sequence that does not require any retrospective correction and that improves quantitative accuracy of multi-slice imaging.